Salt-bath furnace



May 15, 1923. 1,454,847

0. A. COLBY SALT BATH FURNACE Filed Jan. 16, 1920 WITNESSES: INVENTOR [mu/{WW I g 4 l y m/m-"M ATi'ORNEY Patented May 15, 1923.

UNITED STATES PATENT OFFICE.

ORA. A. COLBY, OF IRWIN, PENNSYLVANIA, ASSIGNQR TO WESTINGHOUSE ELEGTRIG 8: MANUFACTURING COMPANY, A GORPOR-ATION OF lE'ENN YLV'ANIA.

SALT-BATH FURNACE.

Application filed. January 16, 1920. Serial No. 351,809.

T 0 all whom it may concern Be it known'that I, ORA A. COLBY, a citizen of the United States, and a resident of Irwin, in the county of \Vestmoreland and State of Pennsylvania, have invented a new and useful Improvement in Salt-Bath Furnaces, of which the following is a specification.

My invention relates to electrically-heated apparatus and particularly to electric furnaces.

The object of my invention is to provide means operatively associated with an electrically-heated salt-bath furnace for automatically increasing the current traversing the conducting bath when an article to be heated is placed in said bath, and for causing a current to flow between said article and said bath.

Heretofore, salt-bath furnaces have been used for heat-treating and tempering steel tools, in which the current value was regulated by manuallmeans associated with the transformer and the tool was heated by conducted heat only. The arrangement of circuits embodying my invention permits an increased current to traverse the conducting bath as soon asthe tool is immersed therein and also permits a'current to flow between the tool and the bath, thus materially increasing the energy transformed into heat.

More specifically, my invention embodies a three-phase source of electromotive force, two of the terminals being connected to the two electrodes of the furnace, the third terminal being connected, by suitable conduct-- i'ng means, to the tool itself. As long as the tool is not placed in the bath, the current flowing through the bath will be a singlephase current and have a value determined. by the resistance of the bath and the value of the electro-motive force applied to the electrodes. If the tool, electrically connected as explained above, is placed in the bath, a current will flow between the tool and each electrode, the current carried by each electrode being approximately 73% greater than vbefore. The current flowing through the tool serves also to heat the same by reason of the energy expended in the ohmic resistance of the tool.

In the accompanying single sheet of drawing's, Figure 1 shows a diagram of connections when a four-wire two-phase supply circuit is used to energize a two-phase-threephase transformer, the secondary winding of which is connected to a salt-bath furnace; Fig. 2 shows a diagram of connection when using a three-phase supply circuit and a three-phase transformer, and Fig. 3 shows adiagram of connection for obtaining substantially the same results when using a single-phase supply circuit.

Conductors A, A and B, B of a twophase supply circuit are connected, through a suitable circuit-interrupting device 1, here shown as an electromagnetic circuit breaker, to the terminals of the primary windings 2 and 3 of a transformer 1. A plurality of double-pole, double-throw switches 5, 6 and 7 are so arranged in the primary circuits as to enable a. portion of the turns of the primary windings 2 and 3 to be cut out of the circuit and thus increase the secondary voltage.

Secondary windings 8 and 9 are provided and are so connected as to deliver. a threephase electromotive force, the connections here shown being the so-called Scott-connection. The terminals of the winding 8 are connected, by means of conductors 10 and 11, to the electrodes l2 'and 13 of a salt-bath furnace 14-. The furnace H is a standard commercial article, well known in the art, and hence will be described here only in a general way.

The furnace 14 comprises awell15 formed in a setting of refractory material 16. Two carbon electrodes 12 and 13 are located in the material 16 and project slightly into the well 15. The well 15 is filled with a salt, such as barium chloride or other equally suitable material, which becomes liquid under the influence of heat generated by the passage of a current therethrough.

The outer terminal of the secondary winding 9 is connected, by means of a conductor 17, to one terminal of a suitable switch 18. The other terminal of the switch 18 is connected to a suitable flexible cable which is, in turn, connected to a suitable metallic holding means (not shown), such as tongs, for holding an article 19, such as a steel tool, to be heat treated.

The diagram shown in Fig. 2 is substantially the same as the one shown in Fig. 1 except that a three-phase supply circuit and a standard three-phase transformer are shown. As the other details are similar to those shown in Fig. 1, it is believed that a further description of the diagram shown in Fig. 2 is unnecessary.

In Fig. 3 is shown a diagram of connections when a single-phase supply circuit is used. An electromagnetic change-over switch 20, controlled by a current coil 21 operatively connected to the conductor 17, is

used to change the connections of the electrodes 12 and 13 to the supply-circuit conductors 22 and 23. \Vhen the tool 19 is not in the bath 15, no electromotive force is being generated in the coil 21 and hence the change-over switch 20 is in the position shown in Fig. 3. The current flows from the conductor 22, through the conducting bath 15, to the electrode 12, through the conductor 10, through the change-over switch 20 and through the adjustable rheostat 24 to the conductor 23. If the tool 19 is placed in the bath 15, a current will flow through it from the conductor 23 to the electrode 13 and thence through the conductor 11 to the supply-circuit conductor 22. An electrom0- tive force is induced in the coil 21 and causes a current to flow through the coil of the switch 20. The core and contact-bridging members are raised and the contact bridging member engages the upper set of contact terminals. The electrodes 12 and 13 are nowv connected to the supply-circuit eonductor 22 and the tool 19 is connected to the supply-circuit conductor 23, and the adjustable rheostat 24 is no longer in circuit.

When the connections shown in Figs. 1 and 2 are used, a current, having a value determined by the electromotive force of the coil 8 and the resistance of the circuit, will traverse the circuit comprising conductors 10 and 11, electrodes 12 and13 and the conducting bath 15. If a tool 19' is placed in the bath 15, a current flows through it into the bath 15, the value of which is approximately 7 3% greater than the current which traversed the bath 15 before the insertion of the tool. The current which traverses the electrodes 12 and 13 and the conductors 19 and 11 is also 73% larger than before by reason of the addition of the current from the other phases of the phase source of supply. Hence, a larger amount of energy is transformed into heat which tends to raise the temperature of the bath 15 and of the inserted tool 19. As a current traverses the tool 19, a certain amount of energy is transformed into heat in the tool itself by reason of its ohmic resistance and this heat also aids to raise the temperature of the. article being heat-treated or tempered. As'soon as the article has reached the proper temperature,'it may be withdrawn from the bath and the former value of current again flows. Where a single-phase supply circuit, as shown in Fig. 3, is used, the rheostat 24 may be so adjusted as to cause a current having a value 73% greater than the normal current to flow, upon the placing of an article to be heat-treated in the bath.

It may be noted that I thus provide inherent means for increasing the current through the conducting bath as soon as an article to be heat-treated is placed in the bath and that I provide inherent means for causing a current to traverse the article itself, thus causing an increase in the amount of heat generated and assisting both to maintain the temperature of the bath and to quickly raise the temperature of the article.

Various modifications may be made without departing from the spirit and the scope of my invention, and I desire that only such limitations shall be placed thereon as are imposed by the prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. In an electrically-heated apparatus, the combination with a conducting bath and means for causing a current to traverse said bath continually, of means whereby the insertion of an article in said bath independently of said electrodes inherently causes an increase in the current traversing a portion of said bath and also causes a current to flow through said article.

2. In an electrically-heated apparatus, the combination with a conducting bath, a lurality of electrodes operatively connecte to said bath, and a source of electro-motive force connected to said electrodes, of-means for inherently causing an increased current to flow through a portion of said bath when an article to be heated is inserted in said bath independently of said electrodes.

3. In an electrically-heated apparatus, the combination with a conducting bath, a plurality of electrodes operatively connected to said bath, and a source of electro-motivc force connected to said electrodes, of means whereby the insertion of an article to be heated in said bath, independently of said electrodes, inherently causes a current to traverse said article and simultaneously causes an increase in the current traversing a portion of said bath.

4. In an electrically-heated apparatus, the combination with a conducting bath and means for causing a current to traverse said bath, of means operativelv associated with said first means whereby the insertion of an article to be heated in said bath, independently of said electrodes, inherently causes an increased current to traverse a portion of said bath and simultaneously causes a current to flow between said article and said bath.

5. In an electrically-heatedapparatus, the combination with a source of electromotive force, a conducting bath and a plurality of I electrodes operatively associated with said bath and electrically connected to said source of electro-motive force, of means for so connecting an article placed in said bath, inde pendently of said electrodes, to said source of electromotive force as to substantially increase the current traversing a portion of said bath.

6. In an electrically-heated apparatus, the combination with a conducting bath, of means for causing a current of predetermined value to traverse said bath, and means for causing a substantial increase in the value of the current traversing a portion of said bath when an article to be heated is placed in said bath, independently of said electrodes, said second means being operative to cause a current to flow between said article and said bath.

7. In an electrically-heated apparatus, the combination with a conducting bath, of means for causing a current of predetermined value to traverse said bath, and means for causing an increased current to flow through a portion of said bath and between said bath and an article placed therein, the two currents being substantially equal in value.

In testimony whereof, I have hereunto subscribed my name this 9th day of January 1920.

ORA A. COLBY. 

